Liquid unloading system



L. A. ZARS LIQUID UNLOADING SYSTEM Oct. 21, 1958 Filed Nov. 1, 1955United States Patent LIQUID UNLOADING SYSTEM Leif A. Zars, San Antonio,Tex., assignor to Ethyl Corporation, New York, N. Y., a corporation ofDelaware Application November 1, 1955, Serial No. 544,253

4 Claims. 01. 137-205 This invention relates to the unloading of certainliquid chemical products from tank cars. More specifically, theinvention relates to an improved apparatus for providing highly safe andeffective unloading by the application of vacuum to such liquidproducts.

In the handling of numerous chemical products, it has been the practiceof industry to transfer such liquids by the application of vacuum ratherthan bypositive displacement or positive pressure liquid transportequipment. The reason for such a general approach may be one of several.For example, the liquid being transferred from one vessel to another maybe toxic, or may be flammable or explosive when exposed to theatmosphere. Examples of such fluids for which vacuum transfer is usuallyprovided are organometallic liquid compounds, the pure alkali metalssuch as sodium, and various other products. The most customary orfrequently encountered situation in which the vacuum transfer of largequantities of such liquids is encountered is in the unloading of tankcar shipments of the commodity to storage or weigh tanks. Vacuumtransfer, or at least simply gravity transfer is also used in numeroussubsequent processing operations, but the degrees of flow then involvedare of lower magnitude than in unloading operation.

Heretofore, it has been the practice to apply vacuum to the weigh orreceiving tank which is to receive the liquid commodity being dischargedfrom the incoming tank car, rather than to the tank car itself. In thismanner, a weigh tank served as a trap to render it impossible for theliquid product to be sucked into the vacuum system, and also made itpossible to utilize the same vacuum source for unloading from the weightank proper and transferring to subsequent processing operations.However, in previous installations, a particular difiiculty was that inorder to accomplish the latter objective (apply-1 ing the vacuum to thecontents of the weigh tank for delivery to processing) it was necessarythat the line to the weigh tank extend to the bottom portion thereof soit in turn could be unloaded. The result of this situation,

as will be evident from the later description of the figure, was thatthe effective vacuum applicable to the tank car tank being unloaded wasreduced by the buildup of liquid head as the weigh tank was filled. Inaddition, it frequently happened that despite the customary precautions,that the liquid being unloaded would spill over into the vacuum sourceline and be responsible for certain operating difficulties. If thevacuum was generated by a vacuum pump, a pump designed only for gaseoushandling would be fouled or filled with the liquid product and wouldrequire disassembly and clean out.

Accordingly, an object of the present invention-is to provide new, andimproved apparatus for the transfer from one vessel to another undervacuum of chemical 2,856,950 Patented Oct. 21, 1958 liquid products.More specifically, the object of the invention is to provide apparatusfor transfer of such liquids under vacuum wherein a constant vacuum canbe maintained upon the discharging tank regardless of the level ofliquid transferred in the receiving tank or vessel. A further object isto provide the constant vacuum on the discharging tank but also providefor application at will of the same vacuum to the receiving tank when itis to be discharged. An additional object is to provide positivepreventive means which negate the misdirection of the liquid beingtransferred into the vacuum generating system. Other more specificobjects will appear hereinafter. i

The details of the invention and the preferred embodiment thereof willbe more readily understood from the following discussion and theaccompanying figure, the.

figure being a schematic elevation of-a typical embodiment, the vesselsinvolved being shown in section.

Generally, the invention comprises, in combination, a transfer line forreceiving liquid from a tank to be discharged, a receiving tank, avacuumgenerating means, a

dip line or discharge line from the transfer line into the,

receiving tank, and a vertically extended loop line connecting thevacuum source and the transfer line. The vertical loop line joins thetransfer line ata point at least as far removed from the dischargingtank as the discharge or dip line. In addition the loop line extendsvertically to an elevation such that a column of the liquid equal tosuch elevation wouldexceed the vacuum available, ,expressed as head ofliquid being transferred.

A by-pass line is also generally provided, joining the transfer line andthe vacuum source. This line does not have an elevated portion therein,and joins the transfer line at a point generally adjacent the loop line.A direct vacuum line is also provided, connecting the upper portion ofthe receiving tank space with the vacuum source.

Both the transfer line and discharge lines communicate with theinteriors of the discharging and receiving tanks, at points near thebottoms, respectively. Valves are provided in the transfer line, theloop line, the discharge line, and the by-passv and direct vacuum lines.in operation, vacuum'is initially applied through the loop leg line tothetransfer line with the valves in the discharge line and the directvacuum line closed. The

' valve in the discharge line is then opened, and the liquid apparatusand the method of operation will be more.

clearly understood from the accompanying figure.

Referring to the figure, a discharge vessel or tank 11 and a receivingtank or vessel 21 are shown in customary relationship. Normally, thedischarge tank is of course the tank of a .tank car, and the receivingtank 21 is usually slightly below the level of the discharge tank 11.

The top of the discharge tank 11 communicates with atmospheric pressureby conventional vent means.

valve 19 which is opened during operation. A line. 12 extends into thedischarging tank to a pointat about the bottom thereof for completeemptying and is preferably equipped with a valve 13. A discharge line 14joins the line 12 and extends to the bottom of the receiving tank 21,

a valve 15 being provided in this line. Additional lines,

including a loop line 36, and a by-pass line 37, connect to the line 12,preferably spaced apart from the connec- Generally,

The, vent means customarily includes a vent line 18 and a.

tion of the discharge line 14, and further away from the discharge tank11. These twqlines havecommon termini, but differ in that the loop-line36 forms an overhead loop, the highest point thereof being at anelevation of n feet above the junction Of the transfer line 12 and thedischarge line 14. As explained hereafter, this elevation contributesvery materially to the efiectiveness of all embodiments of theinvention. In preferred embodiments, an enlarged segmentlfi is providedin the loop line 36, located generally between the highest point of theline and the point of connection with the discharge line 14. Both theloop line 36 and the by-pass line 37 are provided with valve means 38,39. The loop line 36 and bypass line 37 are manifolded in avacuum header317, to which is also connected a direct vacuum line 33. The directvacuum line 33, having a valve 34 therein, connects directly to the topportion of the receiving tank 21,

A vacuum inducing-means maintains in operation a vacuum in the vacuumheader 17. A variety of vacuum inducing means may be employed, but aparticularly effective apparatus is a liquid eductor 41 as indicated inthis embodiment. The educt'or 41 in typical operation receives a flowinghydrocarbon or inertliquid stream through line 42 and by convertingpressure head to velocityhead, establishes a vacuum in the header 17.The inert liquid discharged from the eductor is discharged through aline 43. y s

A supplemental feature found in the most preferred embodiments of thisinvention employing a liquid actuated eductor means as described is awash liquid line 44, provided with a valve 45, which can receive a washliquid from line 42, the wash liquid being the hydrocarbon fluid (orother inert liquid) employed to operate the eductor system. i

In preferred forms of the invention, the loop line 36 has therein, asalready disclosed, an enlarged segment 16 removed from the connectionbfthe loop line and the transfer line 12. It ispreferred that thevolumetric capacity of this enlarged segment 16 be equal to the entirevolume of the transfer line'l2. The significance of this segment is thatautomatic disengaging is provided for occasional presence of gas orvapor bubbles. Thus, occasionally leaks can voccur in the valve orconnecting means 13 joiningv the portion of the transfer line 12 whichis between the portioninside the discharging tank 11 and r theconnection with the -loop line 36 The presence of a substantial quantityof gas originating'i-n this part, of course decreases the averagedensity of thefiuid in the transfer line and the enlarged zone 16assures thansuch gas or vapor willbe disengaged without carry over ofliquid through the loop line 36. This desirable effect of a specificallyenlarged zone can also beachieved by providing a loop line sizedsufiicientlyvlarge to provide more volume in the branch extending, tothe highest point from the transfer line, at least as large asfthetransfer line volume.

The operative relationship of the various components of the apparatuswill be further understood by. the following description of an unloadingcycle. Atthe start of operation, the liquid level in the dischargingtank 11 is near the top of the tank, and the receiving tank 21 issubstantially empty or having only a minor quantity of charge alreadytherein. Vacuum is established on the system as follows: the valve 38 tothe loop line 36 is opened, with the valve to the discharge leg 14 tothe receiving tank 21 closed, and the valve 13 in the transfer line 12open. In addition the valve 34 to the vapor space in the receiving tank21 isclosed. Vacuum is rapidly established in the loop line 36 andtransfer line 12, to the degree of vacuum provided by the eductor vacuumsystem. Flow of liquid starts through the transfer line 12 and continuesthrough a portion .of theleg of the loop line 36 butdoes not carry overbut'n'ses to a height H corresponding to the head provided-by thevacuum. Discharge line 14 is concurrently or thereafter. openedby,

opening the valve therein 15, and liquid flow immediately starts throughdischarge line 14 under the influence of the elevation head. Desirably,the loop line 36 valve 38 is then closed and the direct vacuum line 33valve 34 is opened. The pressure in the receiving tank 21 is thussteadily decreased, and flow continues under siphoning action and theincreasing vacuum in the receiving tank. Because flow is established sorapidly, the start up period is appreciably reduced because flow doesnot need to await the removal of copious quantities of gas from theempty receiving tank space.

Flow thus established is continued in this manner, the level of contentsin the discharging tank '11 dropping, and rising in the receiving tank21. If any leaks are encountered in the piping system so that air isentrained with the moving liquid in sufficient quantity to break thesiphon leg, the flow of liquid may be interrupted. In such event, anyliquid height in the loop line 36 automatically feeds back to thedischarge line 14 into the receiving tank 2 1, andthen thefull vacuum ofthe vacuum systemiis immediately reestablishedonthe discharging tank 11by reopening the loop line 36 and flow is re-initiated. In someoperations, this period of the discharging cycle :will I assume anintermittent pulsing effect, that is, slugs of liquidare alternatelyaspirated out of the discharging tank 11 when the full effect of thevacuu nfsource is applied through the loop line 36, and is terminatedwhen .the loop 'line head is again established as before and the effectofthe vacuum thus applied for flow is .temporarily -.elirninat ed. Upon.completion of the unloading cycle, it is necessary to flush out thesystem ,by the liquid employed ,in the vacuum establishing device.Thence, the loop line 36 i s closed by closing the valve therein 38, butthe transfer line valve 13 and the discharge to the discharge line .14are p ren Wa h n tai dsus a al r n t h drocarbon, is fed to the systembyopening the valve 45 in the wash liquid line :44 and closing the.valve 46 controlling operation of the eductor .41. Upon completion offilling with this wash; liquid-the system is again emptied. However,inthispase, sincethewashing liquid is appreciably lower d s t haw the lilt simsrmal handled in the tanks, the-flow ofgliquid is thr oughflhetransfer line 12 .and through ,the entire lgo p line 36 duringan initialportion. of the ,washing ioperation. This washes out the loop line 36 aswe ll .,as; t he discharging n T wa inss r isrsmsl e b r n the valve 38in the-loop line 36 and .op eningthe valve 39inthe-bypass line 37.

,Having fully describedthe apparatus of, the invention, it will-beunderstood that numerous minor variations can be incorporated-withoutdeparting from the scopeof the inventiomas defineddn the followingclaims.

Iclaim: I l. A safety transfer system .for the transfer of a liquid froma discharge tank maintained atatmospheric pressure to a receiving tank,said receiving tankhaving an elevation notgreatervthan the dischargetank, comprising: a transfer line, avertically extendedloop'line, a discharge line, .adirect vacuum line, valves in said loop, discharge, anddirect vacuum vlines, and .auvacuum source; said transfer linecommunicating with theinteriprof the discharge tank near the bottomthereof, said discharge line being connected to the transferline andcommunicating with the interior of the receiving tank near the bottomthereof, said loop lineconnecting to the transfer line at a point atleastras remote from the discharge tank as the discharge line, andconnecting; to saidvacuurn source, the. elevationof thehighest point insaid loop linebeing greater, in headrof liquid being transferred, thanthe head corresponding to the vacuum generated by the vacuum source, andsaiddirect vacuum line communicating withthe upper portion of theinteriprofthe ,receiving tank and the vacuumsource.

The apparatusof claim l further defined in that 5 the loop line has anenlarged segment therein, said segment being between the highest pointin the loop line and the connection with the transfer line, and having avolumetric capacity at least equal to the volume of the transfer line.

3. The apparatus of claim 1 further defined in that the volume of theportion of the loop line, from the connection to the discharge line tothe highest point of the loop line, is greater than the volume of thetransfer line.

4. A safety transfer system for the transfer of a liquid from adischarge tank to a receiving tank, and for cleaning said dischargetank, including a transfer line, a vertically extending loop line, adischarge line, a direct vacuum line, a Wash liquid line, valves in eachof said lines and a vacuum source, said source including an eductorsystem for generating vacuum by flow of an inert liquid, and a vacuummanifold, the transfer line extending from Within the discharge tanknear the bottom thereof to a point generally above the receiving tank,

the discharge line connecting to the transfer line and extending to apoint within the receiving tank and adjacent to the bottom thereof, theloop line connecting to the transfer line at a point at least as remotefrom the discharge tank as the discharge line and connecting to theVacuum manifold, the highest point in said loop line being greater, inhead of liquid being transferred, than the head corresponding to thevacuum generated by the vacuum source, the direct vacuum linecommunicating with the upper portion of the interior of the receivingtank and the vacuum manifold, and the Wash liquid line extending fromthe eductor system to the transfer line and connecting thereto at apoint closer to the discharge tank than the connection with thedischarge line.

References Cited in the file of this patent UNITED STATES PATENTS RyanJune 10, 1884 Paxton July 6, 1954

